Contacts to transition metal dichalcogenide and manufacturing methods thereof

ABSTRACT

A device includes a transition metal dichalcogenide layer having a first edge with a zigzag atomic configuration. A metallic material has a portion overlapping the transition metal dichalcogenide layer. The metallic material has a second edge contacting the first edge of the transition metal dichalcogenide layer.

BACKGROUND

Semiconductor devices are used in a variety of electronic applications,such as personal computers, cell phones, digital cameras, and otherelectronic equipment, as examples. Semiconductor devices are typicallyfabricated by sequentially depositing insulating or dielectric layers,conductive layers, and semi-conductive layers of material over asemiconductor substrate, and patterning the various material layersusing lithography to form circuit components and elements thereon.

Transistors are circuit components or elements that are often formed onsemiconductor devices. Many transistors may be formed on a semiconductordevice in addition to capacitors, inductors, resistors, diodes,conductive lines, or other elements, depending on the circuit design.Field Effect Transistors (FETs) are commonly known transistors.

Generally, a transistor includes a gate stack formed between source anddrain regions. The source and drain regions may include a doped regionof a substrate and may exhibit a doping profile suitable for aparticular application. The gate stack is positioned over the channelregion and may include a gate dielectric interposed between a gateelectrode and the channel region in the substrate.

In recent development of transistors, Transition Metal Dichalcogenide(TMD) materials are used for forming the transistors. The TMD materialsform the active regions, which include the channel regions and sourceand drain regions. However, TMD materials are semiconductor materials,and hence the contact resistance to the source and drain regions ishigh.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 illustrates an atomic structure of a Transition MetalDichalcogenide (TMD) material and semi-conductive edges that can beformed from the TMD material in accordance with some embodiments;

FIG. 2 illustrates an atomic structure of a TMD material and metallicedges that can be formed from the TMD material in accordance with someembodiments;

FIG. 3 illustrates a top view of a TMD region and a contact plugcontacting a top surface and a metallic edge of the TMD region inaccordance with some embodiments;

FIG. 4 illustrates a cross-sectional view of a TMD region and a contactplug contacting a top surface and a metallic edge of the TMD region inaccordance with some embodiments;

FIG. 5 illustrates a top view of a TMD region and a contact plugcontacting a top surface and a zigzag metallic edge of the TMD inaccordance with some embodiments;

FIG. 6 illustrates a perspective view of a transistor formed of a TMDregion and source/drain contact plugs in accordance with someembodiments;

FIGS. 7 through 12 illustrate top views of transistors formed of TMDregions and source/drain contact plugs in accordance with someembodiments;

FIGS. 13 and 14 illustrate a top view and a cross-sectional view,respectively, of a resistor formed of TMD regions in accordance withsome embodiments; and

FIGS. 15 through 18 illustrate an exemplary process for forming TMDlayers with metallic and semi-conductive edges.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “underlying,” “below,”“lower,” “overlying,” “upper” and the like, may be used herein for easeof description to describe one element or feature's relationship toanother element(s) or feature(s) as illustrated in the figures. Thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. The apparatus may be otherwiseoriented (rotated 90 degrees or at other orientations) and the spatiallyrelative descriptors used herein may likewise be interpretedaccordingly.

Transistors and resistors based on Transition Metal Dichalcogenide (TMD)materials and the methods of forming the same are provided in accordancewith various exemplary embodiments. Throughout the various views andillustrative embodiments, like reference numbers are used to designatelike elements.

FIG. 1 illustrates an atomic structure of TMD material 20. TMD materialsinclude a class of materials that have the general chemical formula ofMX₂, wherein M is a transition metal element, and X is a chalcogen. Theexemplary materials of the transition metal M include Ti, V, Co, Ni, Zr,Mo, Tc, Rh, Pd, Hf, Ta, W, Re, Ir, and Pt. Element X may be S, Se, orTe. Exemplary TMD materials include MoS₂, MoSe₂, WS₂, WSe₂, MoTe₂, andWTe₂ in accordance with some exemplary embodiments. TMDs form a layeredstructure with the form X-M-X, wherein the chalcogen atoms X aredistributed in two hexagonal planes separated by a plane of metal atomsX.

In FIG. 1, chalcogen atoms X are distributed as a first plurality ofrows, and transitional metal elements M are distributed as a secondplurality of rows, with the first and the second rows of atomsdistributed alternatingly. The illustrated chalcogen atoms X (a firstplurality of chalcogen atoms) are in a first plane, and the illustratedtransition metal atoms M are in a second plane beneath the first plane.Also, there is a third plane, in which a second plurality of chalcogenatoms X is located. The third plane is further beneath the second plane.In accordance with some embodiments in which TMD material 20 has a 2Hpoly types (with a trigonal prism structure), as illustrated, the secondplurality of chalcogen atoms X is overlapped by the illustrated firstplurality of chalcogen atoms X in a one-to-one correspondence, and henceare not visible in FIG. 1. The first and the second plurality ofchalcogen atoms X and the metal atoms M are bonded together to form amono-layer of TMD through chemical bonds, wherein the mono-layerincludes three planes of atoms. In accordance with alternativeembodiments, TMD material 20 may have other structures such as atrigonal antiprism structure, in which the second plurality of chalcogenatoms X are not overlapped by the illustrated first plurality ofchalcogen atoms X. In accordance with some embodiments of the presentdisclosure, a TMD region may include one or a plurality of mono-layers,wherein the atoms in neighboring mono-layers are attracted to each otherby van der Waals force, rather than chemical bonds.

FIG. 1 further illustrates lines 22A, 22B, and 22C. In the followingdiscussion, line 22A is used as an example. It is appreciated that lines22B and 22C are equivalent lines of line 22A, and hence the discussionregarding line 22A also applies to lines 22B and 22C. In the top view asshown in FIG. 1, the atoms on the left side of and closest to line 22Aform a plurality of armchair patterns (configuration). For example, thetwo columns of atoms marked as 24 form the armchair patterns. Similarly,the atoms on the right side of and closest to line 22A form a pluralityof armchair patterns. Accordingly, when TMD region 20 is cut along line22A and is separated into a left part and a right part, the resultingright edge of the left part is formed of atoms having the armchairpattern, and the resulting left edge of the right part is formed ofatoms having the armchair pattern also. The edges with the armchairpatterns demonstrate semiconductor properties, and are accordinglyreferred to as semi-conductive edges.

In reality, when TMD region is cut along line 22A, the atoms on theresulting edge (wherein the atoms are referred to as edge atomshereinafter) will reconstruct to have different shapes/patterns, andthere is a plurality of possible reconstructed patterns. The edges withthese patterns most likely demonstrate semiconductor properties.Regardless of how the edges are reconstructed, the respective edges arestill referred to as armchair edges or semiconductive edges.Furthermore, regardless of how the edges are reconstructed, when a lineis drawn in an inner region and parallel to the edge, the armchairpattern is clearly visible. For example, FIG. 1 illustrates exemplaryline 26, wherein the two columns of atoms on the left of line 26 mayhave the armchair pattern even if the edges atoms on the right of line26 are reconstructed.

It is realized that lines 22B and 22C are the equivalent lines of line22A. Lines 22A, 22B, and 22C form 60 degree angles and 120 degreeangles. Accordingly, if the cutting is made along line 22B or 22C, theresulting edges of TMD region 20 will also demonstrate semiconductorproperties, and are accordingly referred to as armchair edges orsemi-conductive edges.

FIG. 2 further illustrates lines 28A, 28B, and 28C of the same TMDmaterial 20. In the following discussion, line 28A is used as anexample. It is appreciated that lines 28B and 28C are equivalent linesof line 28A, and hence the discussion regarding line 28A also applies tolines 28B and 28C. In the top view as shown in FIG. 2, the atoms on theupper side of and closest to line 28A form a plurality of zigzagpatterns. For example, the two rows of atoms marked as 30 form a zigzagpattern (configuration). Similarly, the atoms on the lower side of andclosest to line 28A form a zigzag pattern. Accordingly, when the TMDregion 20 is cut along line 28A and is separated into an upper part anda lower part, the resulting bottom edge of the upper part is formed ofatoms having a zigzag pattern, and the resulting top edge of the lowerpart is formed of atoms having a zigzag pattern also. The edges with thezigzag pattern demonstrate metallic (conductive) properties, and areaccordingly referred to as metallic edges.

In reality, when TMD region is cut along line 28A, the edge atoms willalso reconstruct to have different shapes/patterns, and there is aplurality of possible reconstructed patterns. The edges with thesepatterns most likely demonstrate metallic properties. Regardless of howthe edges are reconstructed, the respective edges are still referred toas zigzag edges or metallic edges. Furthermore, regardless of how theedges are reconstructed, when a line is drawn in an inner region andparallel to the edge, the zigzag pattern is clearly visible. Forexample, FIG. 2 illustrates exemplary line 32, wherein the two rows ofatoms below line 32 may have the zigzag pattern even if the atoms overline 32 are reconstructed.

It is realized that lines 28B and 28C are the equivalent lines of line28A. Lines 28A, 28B, and 28C form 60 degree angles and 120 degreeangles. Accordingly, if the cutting is made along line 28B or 28C, theresulting edges of the TMD region 20 will also demonstrate metallicproperties, and are accordingly referred to as metallic edges. As aresult of the metallic properties, when contact plugs are in contactwith the metallic edges, the contact resistance is very low comparing tothe contact resistance between contact plugs and the semi-conductiveedges or the top surface and bottom surface of the TMD mono-layer. Themetallic edges may be, for example, sulfur-terminated (−1,0,1,0) edgesand/or molybdenum-terminated (1,0,−1,0) edges.

FIGS. 3 and 4 illustrate a top view and a cross-sectional view,respectively, of a contact between contact plug 34 and TMD layer 20.Referring to FIG. 3, TMD region 20 is located on dielectric layer 36.Dielectric layer 36 may be formed of a material comprising, but notlimited to, silicon oxide (SiO₂), hafnium oxide (HfO₂), zirconium oxide(ZrO₂), aluminum oxide (Al₂O₃), a nitride such as silicon nitride, anoxynitride such as silicon oxynitride, a carbide such as siliconcarbide, or other dielectric materials.

TMD layer 20 is formed over and in contact with the top surface ofdielectric layer 36. TMD layer 20 may be a mono-layer of TMD or mayinclude a fewer mono-layers. TMD layer 20 may be formed using ChemicalVapor Deposition (CVD), with MoO₃ and a sulfur-containing gas such assulfur vapor or H₂S as process gases and N₂ as a carrier gas. Theformation temperature may be between about 600° C. and about 700° C. inaccordance with some exemplary embodiments, and higher or lowertemperatures may be used. The process conditions are controlled toachieve the desirable total count of mono-layers. In accordance withalternative embodiments, Plasma Enhanced Chemical Vapor Deposition(PECVD) or other applicable methods are used. For example, TMD layer 20may be formed from a flake of MX₂, which is mechanically exfoliated froma bulk MX₂ crystal, and transferred onto dielectric layer 36.

Contact plug 34 is formed in dielectric layer 35, which is sometimesreferred to as an Inter-Layer Dielectric (ILD). Contact plug 34 is incontact with an edge of TMD layer 20. Furthermore, contact plug 34 mayinclude a bottom surface (as shown in FIG. 4) contacting a top surfaceof TMD layer 20. Contact plug 34 is a metallic contact plug inaccordance with some embodiments of the present disclosure, whichincludes a metal. The available materials of contact plug 34 includeelemental metallic materials such as tungsten (W), copper (Cu), tantalum(Ta), titanium (Ti), aluminum (Al), hafnium (Hf), molybdenum (Mo),scandium (Sc), yttrium (Y), nickel (Ni), platinum (Pt), or combinationsthereof. Contact plug 34 may have a low work function lower than 4.6 eV,for example. In accordance with some exemplary embodiments of thepresent disclosure, contact plug 34 is formed of a metallic nitride suchas tantalum nitride (TaN), titanium nitride (TiN), tungsten nitride(WN), molybdenum nitride (MoN), etc. In accordance with otherembodiments of the present disclosure, contact plug 34 is formed of aconductive metal oxide such as molybdenum oxide (MoO₃), ruthenium oxide(RuO₂), indium tin oxide, etc. Contact plug 34 may be formed by adeposition method such as CVD, Atomic Layer Deposition (ALD), or PVD.

Referring to the cross-sectional view shown in FIG. 4, edge 34A ofcontact plug 34 is in contact with edge 20M of TMD layer 20, whereinedge 20M is a metallic edge. As illustrated in FIG. 1, the metallicedges of TMD layer 20 are parallel to the atoms forming zigzag patterns.Accordingly, edge 34A of contact plug 34 is also parallel to the zigzagpatterns of the atoms in TMD layer 20. Throughout the description, thedashed lines are used to represent the metallic edges of the TMD layers.In addition, the reference notations of the metallic edges includeletter “M” following a reference number.

As shown in FIG. 4, a bottom surface of contact plug 34 and a topsurface of TMD layer 20 are in contact with each other to form ametal-to-semiconductor interface. Contact plug 34 and the top surface ofTMD layer 20 generally do not react with each other, and the resultingmetal-to-semiconductor interface has a Van Der Waals gap or tunnelbarrier. The presence of this barrier reduces the efficiency in carrierinjection from contact plug 34 into TMD layer 20. Accordingly, thebottom surface of contact plug 34 and the top surface of TMD layer 20 donot form Ohmic contacts, and the contact resistance is high. On theother hand, edge 34A of contact plug 34 contacts the metallic edge 20Mof TMD layer 20, and hence form Ohmic contacts. Accordingly, the contactresistance between edge 34A and 20M is low, which contributes to thesignificant reduction in the overall contact resistance.

FIG. 5 illustrates a top view of contact plug 34 contacting TMD layer 20in accordance with alternative embodiments. This embodiment differs fromthe embodiment in FIG. 4 in that the edge 20M of TMD layer 20 is azigzag edge including a plurality of straight segments. The length ofeach of the straight segment in the zigzag edge 20M may have a lengthgreater than about 1 nm, and may be in the range between about 1 nm andabout 100 nm, or be in the range between about 1 nm and about 10 nm. Thestraight segments of the zigzag edge 20M may be parallel to lines 28A,28B, and/or 28C (FIG. 2), and the straight segments are metallicsegments. The straight segments of TMD layer 20 in FIG. 5 may form 60degree angles with each other. As a result of the zigzag edge 20M, edge34A of contact plug 34 also has a zigzag pattern. Advantageously, byforming zigzag edge 20M, the interface area between TMD layer 20 andcontact plug 34 is increased over the interface area in the embodimentsin FIG. 3. Accordingly, the contact resistance between contact plug 34and TMD layer 20 is further reduced.

FIG. 6 illustrates a perspective view of transistor 38, which is formedover dielectric layer 36. In accordance with some embodiments of thepresent disclosure, transistor 38 includes an active region formed ofTMD layer 20, wherein the active region includes a channel region, andsource region 40 and drain regions 41 on the opposite sides of thechannel region. Gate dielectric 42 and gate electrode 44 are formed overthe channel region. The illustrated TMD layer 20 has one mono-layer,which includes a top layer and a bottom layer formed of chalcogen atoms,and a middle layer formed of transition metal atoms. In accordance withalternative embodiments of the present disclosure, TMD layer 20 includesa plurality of mono-layers. Edge 34A of contact plugs 34 thus maycontact edges 20M of all of the plurality of mono-layers.

As shown in FIG. 6, each of the source and drain contact plugs 34includes a portion having edge 34A, which is in contact with themetallic edge 20M of TMD layer 20. Accordingly, the source/drain contactresistance is advantageously reduced.

FIG. 7 illustrates a top view of transistor 38 in accordance with someembodiments. TMD layer 20 includes metallic edges 20M extending in adirection perpendicular to the channel length direction (the directionconnecting source region 40 and drain region 41). TMD layer 20 alsoincludes semi-conductive edges 20S overlapped by gate dielectric 42 andgate electrode 44. Semi-conductive edges 20S may be parallel to thechannel length direction. Semi-conductive edges 20S may have thearmchair atomic configuration as shown in FIG. 1. With thesemi-conductive edges 20S passing below gate electrode 44, the leakagecurrent between source region 40 and drain region 41 is low.

As a comparison, if the metallic edges passing below gate electrode 44,and the semi-conductive edges contact the edges of contact plugs 34, theleakage will be high, and the contact resistance will be high. This isbecause a metallic edge oriented in the source-to-drain direction wouldconduct (even though a gate line may straddle across the channelregion), leading to substantial off-state leakage between the sourceregion and the drain region of a transistor having a TMD channel.Therefore, the structure shown in FIG. 7 is more suited for transistors.

FIG. 8 illustrates a top view of transistor 38 in accordance withalternative embodiments. These embodiments are similar to theembodiments in FIGS. 6 and 7. In addition to the features shown in FIGS.6 and 7, openings 46 are formed in TMD layers 20, and penetrate throughTMD layer 20. The top-view shapes of openings 46 may be triangles,rectangles, hexagons, any other polygons, or irregular shapes. Contactplugs 34 may completely or partially overlap (and penetrate into)openings 46. As a result, contact plugs 34 extend into and penetratethrough TMD layer 20 to contact dielectric layer 36. The portions ofcontact plugs 34 are referred to as the via portions of contact plugs 34hereinafter.

FIG. 8 illustrates that some of exemplary edges 20M in openings 46 arefully in contact with contact plugs 34, while some other edges 20M havefirst portions in contact with one of the contact plugs 34, and secondportions not in contact with any contact plug 34. The second portionsthus do not contribute to the reduction of contact resistance. There mayalso be an entire edge of opening that is not in contact with anycontact plug 34, as also shown in FIG. 8.

In accordance with some embodiments of the present disclosure, at leastone, and may be more or all of the edges of openings 46 are metallicedges. These metallic edges 20M are in contact with the edges of the viaportions of contact plugs 34. Accordingly, the Ohmic contact interfacearea between contact plugs 34 and source/drain regions 40/41 is furtherincreased, and contact resistance is further reduced.

In accordance with some embodiments of the present disclosure, openings46 are formed by a masked ion bombardment on TMD layer 20, followed by awet or dry etching to remove some portions of TMD layer 20, leavingopenings 46. The ion bombardment involves the introduction of energeticions of argon, germanium, silicon (or any other element or molecularions), which incur damage to the two-dimensional crystal structure ofTMD layer 20. Such crystal defects are weak spots where materials can beremoved during wet etching, dry etching, or exposure to a reactive gas.For example, a dry plasma etching may be performed in an oxygen orfluorine-containing plasma to form openings 46. The dry etching can alsobe performed using xenon difluoride (XeF₂). Annealing TMD layer 20 withdefects in an oxygen-containing ambient at temperatures above 300degrees Celsius may also lead to the formation of triangular openings46. The edges of openings 46 may be optionally passivated, e.g. byannealing in a sulfur-containing gas such as hydrogen sulfide (H₂S). Inalternative embodiments, in the formation of openings 46, the masked ionbombardment is skipped, while a wet etching, a dry etching, or areactive gas exposure is performed.

FIG. 9 illustrates a top view of transistor 38 in accordance with yetalternative embodiments. These embodiments are similar to theembodiments in FIG. 8, except openings 46 in TMD layer 20 include bothsemi-conductive edges 20S and metallic edges 20M. Although the contactresistance between semi-conductive edges 20S and contact plugs 34 ishigher than the contact resistance between metallic edges 20M andcontact plugs 34, semi-conductive edges 20S and contact plugs 34 stillcontribute to the increased interface areas, and still contribute to thereduction of contact resistance.

FIGS. 10 through 12 illustrate the top views of transistors 38A and 38B,which share a common source or a common drain. In accordance with someembodiments of the present disclosure, the common sourced/drain regionis a common drain region. The concept of the present disclosure isreadily applicable to the transistors with a common source region.

Referring to FIG. 10, a continuous TMD layer 20 is shared by transistors38A and 38B, and forms the channel regions and the source/drain regionsof transistors 38A and 38B. Transistor 38A includes gate electrode 44A,which crosses semi-conductive edges 20S of TMD layer 20. Transistor 38Bincludes gate electrode 44B, which crosses semi-conductive edges 20S ofTMD layer 20. This results in the advantageous reduction of leakagecurrent between source and drain regions.

Contact plug 34B contacts three metallic edges 20M. Accordingly, thecontact resistance between contact plug 34B and source region 40A issmall. Two of metallic edges 20M in contact with contact plug 34B areparallel with each other, and the other metallic edge 20M join the twoparallel edges 20M, with angle α being 60 degrees. Similarly, contactplug 34C is in contact with three metallic edges 20M of source region40B, and hence the contact resistance between contact plug 34C andsource region 40B is small.

Drain region 41 is the common drain region shared by transistors 38A and38B. Drain contact plug 34D includes edges 34A in contact with edges 20Mof TMD layer 20. Accordingly, the contact resistance between draincontact plug 34D and the common drain region 41 is low. Furthermore,edges 20M underlying drain contact plug 34D is neither parallel norperpendicular to the lengthwise direction of gate electrodes 44A and44B.

In addition, openings 46 may be formed in source regions 40A and 40Band/or drain region 41. Source regions 40 and/or drain region 41 havemetallic edges 20M inside openings 46. As a result, contact plugs 34B,34C, and 34D may extend into openings 46 to contact the metallic edges20M, and hence the contact resistance between contact plugs 34B, 34C,and 34D and the respective source and drain regions is further reduced.

FIG. 11 illustrates transistors 38A and 38B in accordance with yetalternative embodiments. These embodiments are similar to theembodiments in FIG. 10, except each of contact plugs 34B and 34C is incontact with a single, rather than three metallic edges 20M. Althoughthe transistors in these embodiments have higher source contactresistance than the embodiments in FIG. 10, the area occupied by thetransistors in accordance with these embodiments may be smaller.

FIG. 12 illustrates transistors 38A and 38B in accordance with yetalternative embodiments. These embodiments are similar to theembodiments in FIG. 11, except drain contact plug 34D is in contact withsemi-conductive edges 20S, rather than metallic edges 20M. Although thetransistors in these embodiments have a higher drain contact resistancethan the embodiments in FIG. 11, the area occupied by the transistors inaccordance with these embodiments may be smaller.

FIG. 13 illustrates a top view of resistor 48 in accordance with someexemplary embodiments. Resistor 48 is formed over dielectric layer 36.Resistor 48 includes at least one, and possible a plurality of TMDstrips 120. TMD strips 120 may be formed of essentially the samematerial as that of TMD layers 20 shown in FIGS. 1 and 2. The shape andthe sizes (such as length and widths) of TMD strips 120 may be differentfrom each other or identical to each other. Metallic edges 20M of TMDstrips 120 are in the lengthwise directions of TMD strips 120. Width W1of TMD strips 120 may be smaller than about 20 nm, or smaller than about10 nm. Length L1 of the interface between TMD strips 120 and contactplugs 34E and 34F may be greater than about 10 nm. Contact plugs 34E and34F are formed on the opposite ends of TMD strips 120. The portions ofTMD strips 120 between contact plugs 34E and 34F are the resistiveportions of the resistor.

FIG. 14 illustrates a cross-sectional view of the structure shown inFIG. 13, wherein the cross-sectional view is obtained from the planecontaining line 14-14 in FIG. 13. Contact plugs 34E and 34F have bottomsurfaces contacting the top surfaces of TMD strips 120, and edgescontacting the metallic edges 20M of TMD strips 120. Contact plugs 34Eand 34F are formed in dielectric layer 35 in some embodiments.Accordingly, the contact resistance of the resistor 48 is significantlyreduced due to the interface between contact plugs 34E and 34F andmetallic edges 20M. Furthermore, the contact resistance is inverselyproportional to the number of TMD strips 120, and hence increasing thenumber of TMD strips 120 advantageously reduces the contact resistance.

FIGS. 15 through 17 illustrate an exemplary process for forming TMDlayers having the intended metallic and semi-conductive edges. Referringto FIG. 15, TMD layer 20 is formed over dielectric layer 36 as a blanketlayer. Next, a Scanning Tunneling Microscopy (STM) is used to determinethe distribution of atoms in TMD layer 20, and find out the orientationsof the atoms in TMD layer 20. The directions of the semi-conductiveedges and metallic edges thus are found.

Next, as also shown in FIG. 15, STM tip 50 is brought close to thesurface of TMD layer 20, with a voltage (for example, between about 2Vand about 5V) applied on STM tip 50. Accordingly, the portion of TMDlayer 20 under STM tip 50 is removed. STM tip 50 is moved in a desirabledirection to generate a metallic edge or a semi-conductive edge,depending on the requirement of the resulting device. FIG. 16illustrates an exemplary embodiment in which the resulting edges aremetallic edge 20M. Semi-conductive edges may also be formed using STMtip 50.

Next, as shown in FIG. 17, a photo lithography process is performed.Photo resist 52 is applied to protect the desirable portions of TMDlayer 20, and the undesirable portions of TMD layer 20 are exposed. Theundesirable portions are then removed in an etching process, leaving thestructure as shown in FIG. 18. Photo resist 52 is then removed. By usingthe STM tip to form the desirable metallic and semi-conductive edges,the process margin of the etching process is increased, so that even ifthe photo lithography process may not have the atom-level accuracy, thesemi-conductive edges and metallic edges may still be formed. Inalternative embodiments, the cutting using the STM tip is skipped.

The embodiments of the present disclosure have some advantageousfeatures. By forming contact plugs to contact the metallic edges of theTMD materials, the contact resistance is significantly reduced. On theother hand, semi-conductive edges may be used in certain places such asunderlying the gate electrode to reduce the leakage current.

In accordance with some embodiments of the present disclosure, a deviceincludes a transition metal dichalcogenide layer having a first edgewith a zigzag atomic configuration. A metallic material has a portionoverlapping the transition metal dichalcogenide layer. The metallicmaterial has a second edge contacting the first edge of the transitionmetal dichalcogenide layer.

In accordance with alternative embodiments of the present disclosure, adevice includes a dielectric layer, and a transition metaldichalcogenide layer overlying the dielectric layer. The transitionmetal dichalcogenide layer has a metallic edge. A contact plug has afirst portion overlapping the transition metal dichalcogenide layer, anda second portion misaligned with the transition metal dichalcogenidelayer. The second portion of the contact plug has an edge in contactwith the metallic edge of the transition metal dichalcogenide layer.

In accordance with alternative embodiments of the present disclosure, adevice includes a transition metal dichalcogenide layer. The transitionmetal dichalcogenide layer includes a source region having a first edgewith a first zigzag atomic configuration, a drain region having a secondedge with a second zigzag atomic configuration, and a channel regionbetween the source region and the drain region. The channel region hastwo opposite edges having an armchair atomic configuration. The devicefurther includes a source contact plug having a first bottom surfacecontacting a top surface of the source region, and a third edgecontacting the first edge. The device further includes a drain contactplug having a second bottom surface contacting a top surface of thedrain region, and a fourth edge contacting the second edge.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A device comprising: a transition metaldichalcogenide layer comprising a first edge having a zigzag atomicconfiguration; and a metallic material having a portion overlapping thetransition metal dichalcogenide layer, wherein the metallic materialcomprises an edge contacting the first edge of the transition metaldichalcogenide layer.
 2. The device of claim 1, wherein the metallicmaterial further comprises a bottom surface contacting a top surface ofthe transition metal dichalcogenide layer.
 3. The device of claim 1further comprising: a Field-Effect Transistor (FET) comprising: a gatedielectric overlapping a middle portion of the transition metaldichalcogenide layer, wherein the transition metal dichalcogenide layercomprises a first source/drain region and a second source/drain region,with the first edge being an edge of the first source/drain region; anda gate electrode overlying the gate dielectric.
 4. The device of claim3, wherein the transition metal dichalcogenide layer further comprises asecond edge extending from the first source/drain region to the secondsource/drain region, with the second edge having a portion overlapped bythe gate electrode, wherein the second edge has an armchair atomicconfiguration.
 5. The device of claim 3, wherein the first source/drainregion further comprises a third edge contacting the metallic material,wherein the third edge is neither parallel nor perpendicular to thefirst edge, and the third edge has a zigzag atomic configuration.
 6. Thedevice of claim 3, wherein the second source/drain region furthercomprises two edges parallel with each other and contacting edges of acontact plug of the FET, wherein the two edges are neither parallel norperpendicular to the first edge.
 7. The device of claim 3, wherein thefirst source/drain region further comprises an opening penetratingthrough the transition metal dichalcogenide layer, with the metallicmaterial comprising a via portion penetrating through the opening,wherein the transition metal dichalcogenide layer comprises portions onopposite sides of the opening, and wherein the transition metaldichalcogenide layer comprises at least a metallic edge in the opening.8. The device of claim 7, wherein the transition metal dichalcogenidelayer fully encircles the opening.
 9. The device of claim 1, wherein thetransition metal dichalcogenide layer forms a part of a resistor, withthe metallic material further contacting the first edge to form acontact to an end of the resistor.
 10. A device comprising: a dielectriclayer; a transition metal dichalcogenide layer overlying the dielectriclayer, wherein the transition metal dichalcogenide layer comprises afirst metallic edge; and a contact plug having a first portionoverlapping the transition metal dichalcogenide layer, and a secondportion misaligned with the transition metal dichalcogenide layer,wherein the second portion of the contact plug has an edge in contactwith the first metallic edge of the transition metal dichalcogenidelayer.
 11. The device of claim 10, wherein the transition metaldichalcogenide layer comprises: a transitional metal element selectedfrom the group consisting of Ti, V, Co, Ni, Zr, Mo, Tc, Rh, Pd, Hf, Ta,W, Re, Ir, and Pt; and a chalcogen selected from the group consisting ofS, Se, and Te.
 12. The device of claim 10, wherein the first metallicedge has a zigzag atomic configuration.
 13. The device of claim 10,wherein the second portion of the contact plug is in physical contactwith the dielectric layer.
 14. The device of claim 10, wherein thecontact plug comprises a via portion penetrating through the transitionmetal dichalcogenide layer to contact the dielectric layer, with the viaportion of the contact plug fully encircled by the transition metaldichalcogenide layer, wherein the via portion of the contact plugcontacts a metallic edge of the transition metal dichalcogenide layer.15. The device of claim 14, wherein the first metallic edge of thetransition metal dichalcogenide layer has zigzagged straight segments,with each of the zigzagged straight segments having a length greaterthan about 1 nm.
 16. A device comprising: a transition metaldichalcogenide layer comprising: a source region comprising a first edgehaving a first zigzag atomic configuration; a drain region comprising asecond edge having a second zigzag atomic configuration; and a channelregion between the source region and the drain region, wherein thechannel region comprises two opposite edges having an armchair atomicconfiguration; a source contact plug comprising a first bottom surfacecontacting a top surface of the source region, and a third edgecontacting the first edge; and a drain contact plug comprising a secondbottom surface contacting a top surface of the drain region, and afourth edge contacting the second edge.
 17. The device of claim 16,wherein the first edge and the second edge are neither parallel to norperpendicular to the two opposite edges of the channel region.
 18. Thedevice of claim 16, wherein the source region further comprises a fifthedge contacting an additional edge of the source contact plug, with thefifth edge and the first edge joined with each other, wherein the fifthedge has a zigzag atomic configuration.
 19. The device of claim 16,wherein the drain region further comprises a sixth edge contacting anadditional edge of the drain contact plug, with the sixth edge and thesecond edge parallel to each other, wherein the sixth edge has a zigzagatomic configuration.
 20. The device of claim 16, wherein one of thesource contact plug and the drain contact plug comprises a via portionpenetrating through the transition metal dichalcogenide layer, with thevia portion fully encircled by the transition metal dichalcogenidelayer, wherein the via portion of the one of the source contact plug andthe drain contact plug contacts a metallic edge of the transition metaldichalcogenide layer.